1. Field of the Invention
This invention relates to the inhibition of corrosion of high lead solder exposed to aqueous systems.
2. Description of the Prior Art
The use of high lead solder, defined as those solders having about 95 percent by weight or more lead content with the remainder tin or tin and silver, is a relatively new development in the fabrication of heat exchange devices, particularly radiators, for use in the cooling system of internal combustion engines. The corrosion of high lead solder, as measured by weight losses under corrosion test conditions, is particularly severe as compared with ordinary lead-tin solders having no more than about 70 percent by weight lead content and the remainder tin and other metals.
Organic phosphates are known as components of corrosion resistant antifreeze compositions from U.S. Pat. Nos. 3,607,757; 4,209,487; and 3,282,846. In each of these references, an organic phosphate is disclosed for use either alone or in combination with other known corrosion inhibitors to inhibit the corrosion of metals in contact with aqueous liquids. In no one of the references is there any disclosure that high lead solder corrosion as the result of contact with an aqueous liquid can be inhibited utilizing the alkali metal aliphatic phosphonates disclosed by the applicant.
Other references disclosing organic phosphates or phosphonic acids or the use of such materials as corrosion inhibitors for metals in contact with aqueous liquids are U.S. Pat. Nos. 4,217,216; 4,246,030; 4,206,156; and 4,163,733.